Vitamin D is important for optimal reproductive function in both animals and humans. It has long been known that serum vitamin D level is important for reproductive function in various animals, but now researchers from the University of Copenhagen and Copenhagen University Hospital have shown that this relationship can also be demonstrated in humans. A new study conducted in 300 normal men showed a positive correlation between the percentage of motile sperm and serum vitamin D levels. The study was recently published in the scientific journal Human Reproduction, and showed additionally that stimulation of human spermatooza in the laboratory with activated vitamin D can increase their forward movement.